The broad and long-term objective of our research is the mechanistic elucidation of key reaction steps of mono- di- and tri-nuclear copper enzymes that activate O2. The methodology used is that of the synthetic analog approach to the active sites of metallobiomolecules, whereby low molecular weight complexes are synthesized and examined at a small molecule level of detail to reveal intrinsic properties uncoupled from the influences of the protein matrix. Synthetic copper complexes can provide mechanistic details of biological reactions if appropriate attention is directed to the ligation environment. Appropriate ligation can elicit particular chemical reactivity while precluding deleterious bimolecular reactions of nascent Cu-O2 intermediates in a homogenous solution. Creation of a mechanistically faithful and a spectroscopically congruent model provides chemical precedent for a particular oxidative mechanism that can be examined at a small molecule level of detail. . Structural, spectroscopic and reactivity characterization of [(LPDA)Cul(MeCN)]1+-O2 products using simple peralkylated diamine ligands, L PDA, will provide chemical precedence for possible biological Cu-O2 intermediates and spectroscopic benchmarks by which such intermediates may be identified. . Spectroscopically congruent models of the binuclear copper enzyme tyrosinase display phenolate monooxygenase reactivity similar to the enzyme. Spectroscopic and kinetic studies of trapped reaction intermediates will provide a more complete mechanistic understanding of this reaction that is the first step in melanin production. . The postulated tyrosinase active oxidant (Cu ll-O2, P) is potentially in equilibrium with an isoelectronic species (Cu Ill- 02, O). Defining the reactivity behavior of each isomer will address an overarching question of whether the 3+ oxidation state of copper is biologically relevant in binuclear copper sites. . Spectroscopic and functional models of galactose oxidase (GOase) will probe the chemical reactivity of Cuphenoxyl species. . A structurally defined trinuclear copper complex will be spectroscopically and magnetically characterized for features similar to the native intermediate in the multi-copper oxidase enzymes. Ceruloplasmin, the major copper-containing enzyme in human blood, is a multi-copper oxidase that is involved in the trafficking of iron (ferroxidase activity).